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Date: Wed, 30 Apr 2014 15:44:30 +0200 (CEST)
From: Lukáš Czerner <lczerner@...hat.com>
To: "Theodore Ts'o" <tytso@....edu>
cc: Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 6/7] mke2fs: check for pre-existing file system
On Wed, 30 Apr 2014, Lukáš Czerner wrote:
> Date: Wed, 30 Apr 2014 13:50:13 +0200 (CEST)
> From: Lukáš Czerner <lczerner@...hat.com>
> To: Theodore Ts'o <tytso@....edu>
> Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>
> Subject: Re: [PATCH 6/7] mke2fs: check for pre-existing file system
>
> On Sat, 26 Apr 2014, Theodore Ts'o wrote:
>
> > Date: Sat, 26 Apr 2014 20:00:33 -0400
> > From: Theodore Ts'o <tytso@....edu>
> > To: Ext4 Developers List <linux-ext4@...r.kernel.org>
> > Cc: Theodore Ts'o <tytso@....edu>
> > Subject: [PATCH 6/7] mke2fs: check for pre-existing file system
> >
> > Warn the system administrator if there is an existing file system on
> > the block device, and give the administrator an opportunity to abort
> > the mkfs operation.
> >
> > Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> > ---
> > misc/mke2fs.c | 4 +++-
> > misc/util.c | 29 +++++++++++++++++++++++++++++
> > misc/util.h | 1 +
> > 3 files changed, 33 insertions(+), 1 deletion(-)
> >
> > diff --git a/misc/mke2fs.c b/misc/mke2fs.c
> > index 799132a..3694ce5 100644
> > --- a/misc/mke2fs.c
> > +++ b/misc/mke2fs.c
> > @@ -1753,7 +1753,9 @@ profile_error:
> > profile_get_integer(profile, "options", "proceed_delay", 0, 5,
> > &proceed_delay);
> >
> > - if (!check_plausibility(device_name, CREATE_FILE,
> > + /* The isatty() test is so we don't break existing scripts */
> > + if (!check_plausibility(device_name, CREATE_FILE |
> > + (isatty(0) ? CHECK_FS_EXIST : 0),
> > &is_device) && !force)
> > proceed_question(proceed_delay);
> >
> > diff --git a/misc/util.c b/misc/util.c
> > index afb0058..be16ebe 100644
> > --- a/misc/util.c
> > +++ b/misc/util.c
> > @@ -113,6 +113,9 @@ int check_plausibility(const char *device, int flags, int *ret_is_dev)
> > int fd, is_dev = 0;
> > ext2fs_struct_stat s;
> > int fl = O_RDONLY;
> > + blkid_cache cache = NULL;
> > + char *fs_type = NULL;
> > + char *fs_label = NULL;
> >
> > if (flags & CREATE_FILE)
> > fl |= O_CREAT;
> > @@ -148,6 +151,32 @@ int check_plausibility(const char *device, int flags, int *ret_is_dev)
> > return 0;
> > }
> >
> > + if ((flags & CHECK_FS_EXIST) && blkid_get_cache(&cache, NULL) >= 0) {
> > + fs_type = blkid_get_tag_value(cache, "TYPE", device);
> > + if (fs_type)
> > + fs_label = blkid_get_tag_value(cache, "LABEL", device);
> > + blkid_put_cache(cache);
> > + }
> > +
> > + if (fs_type) {
> > + if (fs_label)
> > + printf(_("%s contains a %s file system "
> > + "labelled '%s'\n"), device, fs_type, fs_label);
> > + else
> > + printf(_("%s contains a %s file system\n"), device,
> > + fs_type);
> > + free(fs_type);
> > + free(fs_label);
> > + return 0;
> > + }
> > +
> > + /*
> > + * We should eventually replace this with a test for the
> > + * presence of a partition table. Unfortunately the blkid
> > + * library doesn't test for partition tabels, and checking for
> > + * valid GPT and MBR and possibly others isn't quite trivial.
> > + */
>
> That is not true. libblkid definitely can scan for partition or any
> other signature for that matter (lvm, mdraid, ...) and we should
> definitely utilize that.
Take a look at how xfs is doing this:
pr = blkid_new_probe_from_filename(device);
if (!pr)
goto out;
ret = blkid_probe_enable_partitions(pr, 1);
if (ret < 0)
goto out;
ret = blkid_do_fullprobe(pr);
if (ret < 0)
goto out;
/*
* Blkid returns 1 for nothing found and 0 when it finds a signature,
* but we want the exact opposite, so reverse the return value here.
*
* In addition print some useful diagnostics about what actually is
* on the device.
*/
if (ret) {
ret = 0;
goto out;
}
if (!blkid_probe_lookup_value(pr, "TYPE", &type, NULL)) {
fprintf(stderr,
_("%s: %s appears to contain an existing "
"filesystem (%s).\n"), progname, device, type);
} else if (!blkid_probe_lookup_value(pr, "PTTYPE", &type, NULL)) {
fprintf(stderr,
_("%s: %s appears to contain a partition "
"table (%s).\n"), progname, device, type);
} else {
fprintf(stderr,
_("%s: %s appears to contain something weird "
"according to blkid\n"), progname, device);
}
ret = 1;
we should probably also add blkid_probe_enable_superblocks(pr, 1)
even though it is enabled by default but just to better readability.
I think that we probably want to do something similar to this.
Thanks!
-Lukas
>
> It is true that "our" blkid library can not do that, but we should
> actually stop using that and possibly remove it from e2fsprogs since
> it's really out-of-date comparing to upstream libblkid from
> util-linux.
>
> I have some patches to do that, I can revive and resent it.
>
> Thanks!
> -Lukas
>
> > +
> > #ifdef HAVE_LINUX_MAJOR_H
> > #ifndef MAJOR
> > #define MAJOR(dev) ((dev)>>8)
> > diff --git a/misc/util.h b/misc/util.h
> > index 9de3fbf..745568e 100644
> > --- a/misc/util.h
> > +++ b/misc/util.h
> > @@ -20,6 +20,7 @@ extern char *journal_location_string;
> > */
> > #define CHECK_BLOCK_DEV 0x0001
> > #define CREATE_FILE 0x0002
> > +#define CHECK_FS_EXIST 0x0004
> >
> > #ifndef HAVE_STRCASECMP
> > extern int strcasecmp (char *s1, char *s2);
> >
> --
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